﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace jy
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello world");
            Console.WriteLine("请输入圆的半径");
            String sc = Console.ReadLine();
            double sa = double.Parse(sc);
            Console.WriteLine("圆的面积为："+3.14 * (sa*sa));
        }
    }
}
